The invention relates to the field of automotive electrical systems. Specifically, the invention is directed to a method and apparatus for preventing a stall condition in a starter/alternator equipped I.C. engine system.
A recent trend in automotive electrical systems is the combining of the formerly separately functioning and operating starter and alternator/generator components. As automobiles become more electronics intensive, in terms of electronic accessories and sophistication of control systems, the need becomes greater for increased electrical supply. As a result, the alternator has become physically larger and more powerful as automotive electrical needs have increased.
In addition, the need for increasing operating efficiencies from I.C. engines mandates a powerful and frequently operated starter motor to resume I.C. engine operation on short demand cycles. And, while these separate trends have been in place, a third element always present in automotive design is packaging efficiency in terms of underhood space. As these trends have progressed, a commonly proposed strategy is to combine the starter and alternator/generator into a single underhood element. In this regard, the starter function of the starter/alternator can be quite powerful vis-à-vis the I.C. engine being started inasmuch as the I.C. engine is required to achieve self-sustaining operation within xc2xd to 1 second of starter initiation. Likewise, the generator function of the starter/alternator can be equally powerful vis-à-vis the capacity of the I.C. engine to generate sufficient torque especially during instances of high relative load and low relative engine speed. In this instance, a stall condition of the I.C. engine can quickly arise if the load generated by the generating function of the starter/alternator is allowed to overwhelm the torque supplied by the I.C. engine. This situation can be unsafe in circumstances where restarting the I.C. engine from a static condition is unfavorable (i.e. a high heat, high load condition). In addition, if the stall condition is repeated successively followed by I.C. engine restart sequences, the starter/alternator can quickly overheat and become inoperable.
The present invention is directed to solving at least one of the potential problems associated with the trend towards combined starter and generator/alternator functions. Specifically, the present invention proposes a method and associated apparatus for sensing an incipient stall condition of the I.C. engine system equipped with a starter/alternator. When a stall onset is detected, the present method disables the generating function of the starter/alternator to restore sufficient I.C. engine speed to eliminate the stall condition. Thereafter, when sufficient I.C. engine speed is detected, the generating function is restored to the starter/alternator. The stall condition can be sensed either directly from a rotation and/or position sensor mounted to the starter/alternator or, alternatively, the stall condition can be sensed from another I.C. engine driven accessory similarly equipped with a rotation and/or speed sensor. Such an accessory may include, but not be limited to, an engine driven cooling fan, the waterpump, A/C compressor, power steering pump, or I.C. engine camshaft. According to the present invention, the stall condition is prevented resulting in continuity of I.C. engine operation and also resulting in preservation of the starter/alternator from excessive use in the starter mode.